1. Field of the Invention
The present invention relates in general to speed control systems, and more specifically, to speed control systems for controlling speed through the use of engine torque and brake torque control.
2. Description of the Related Art
A driver of a vehicle while traveling along various roads, inclinations, or reversing a vehicle attached to a trailer may find themselves managing multiple tasks in addition to manipulating the accelerator and brake pedals to maintain a desired speed. Such tasks arise because often road surfaces have obstacles (i.e., trees, narrowed pathways, boat launch) which require the driver to concentrate on avoiding them more than on applying a respective force to the acceleration pedal. But more times than not, too much acceleration force is applied and the driver must switch between the acceleration pedal and the brake pedal to maintain the desired speed, often resulting in surging and stopping of the vehicle. This multi-tasking may distract the driver from concentrating on the driving task (i.e., parallel parking, backing a trailer in stall/garage, or backing a boat trailer onto a boat launch dock) or adjusting to various road conditions surrounding the vehicle because the driver is concentrating on operating the accelerator and brake pedals to maintain a desired vehicle speed. Thus, it is desirable to provide some assistance to a vehicle driver, especially one towing a trailer, with maintaining a vehicle speed while the driver concentrates on the road or parking lot conditions.
Conventional cruise control systems try to maintain the preselected speed of a vehicle, whether on flat, ascending or descending grades. These conventional systems typically only work when the vehicle is traveling above a certain threshold speed, such as forty-five miles per hour. With such cruise control systems, as the vehicle transitions up an ascending grade, the throttle is increased to maintain the vehicle at the preselected speed. However, if the cruise control system is active while the vehicle is transitioning down an inclination, the actual vehicle speed may increase beyond that of the speed set by the cruise control. In response, the cruise control system will decrease the throttle in order to reduce the engine torque thereby attempting to reduce the speed of the vehicle. The conventional cruise control system has no other self-means of reducing the actual speed of the vehicle to attain the lower vehicle target speed other than to reduce the torque of the engine. If, even with the reduced engine torque, the descent of the vehicle results in an actual speed greater than the set cruise control speed, the vehicle continues traveling down the descent at the higher speed until either the road surface changes grades or the driver applies the vehicle brakes.
Other types of vehicle speed control systems utilize braking descent systems to maintain the desired vehicle speed while transitioning down an inclination. These systems set a target speed to the vehicle speed as controlled by the brake pedal or the accelerator pedal when the vehicle speed control system is activated. These types of systems may be employed in heavy trucks to help maintain a desired speed when traveling down a descending grade. Again, these are systems for controlling a vehicle traveling at a relatively high rate of speed. These hill descent control systems utilize a single predetermined speed threshold, and when activated, the system determines whether to apply braking or release braking depending on the whether the actual vehicle speed is above or below the predetermined threshold.
When traveling at a relatively low speed, especially when maneuvering with a trailer, even if modified to work at low speeds, it is not practical to set buttons on these cruise control systems to maintain a constant speed. Moreover, even at low vehicle speed, the driver cannot just move the accelerator pedal to a predetermined position to cause the vehicle to travel at a give rate of speed because the vehicle speed does not just depend upon the amount of engine torque but also on the incline of the road surface. Thus, the driver is still required to manipulate the accelerator and brake pedals while also concentrating on maneuvering the vehicle, and possibly a trailer, for avoiding obstacles when traveling at a low rate of speed.